A single-panel projector (see Patent Document 1) is one example of a field sequential color image display device. Such a single-panel projector has a light source, a color wheel, a digital mirror device (DMD), and a projection optical system.
The color wheel has a wheel unit that is provided with a red filter region, a green filter region, and a blue filter region, and is configured such that by rotating this wheel, white light from the light source sequentially irradiates each color filter region to sequentially emit red (R) light, green (G) light, and blue (B) light. The light (RGB) emitted by this color wheel is irradiated upon the DMD.
The DMD has a plurality of micromirrors, each micromirror forming a pixel. The micromirrors are configured such that the angle of each changes in accordance with the drive voltage, the reflection angle differing when a drive voltage that indicates the ON state is supplied and when a drive voltage that indicates the OFF state is supplied. The incident luminous flux is spatially modulated to form an image by the ON/OFF control of each micromirror in accordance with a video signal.
The image-forming operation of the DMD is carried out in synchronization with the rotation operation of the color wheel. The DMD sequentially forms red images, green images, and blue images on the basis of image frames that correspond to each of the colors of red, green and blue. The projection optical system enlarges and projects upon a screen the red images, green images, and blue images that are formed by the DMD.
The frame interval of a single image frame is normally 1/60 second. The color wheel makes one rotation with each image frame (3600 rpm). There are six color subframes during each frame frequency interval, these each being red, green, blue, red, green, and blue. Color-separated light is sequentially irradiated into the DMD according to these six color subframes. On the screen, a red image, green image, blue image, red image, green image, and blue image are sequentially displayed in the interval of 1/60 second, and a full-color image is perceived by the superposition of the afterimages of these images.
In a field sequential color image display device as described above, a phenomenon referred to as color breaking is known to occur. This color breaking phenomenon is a phenomenon in which afterimages of each of the colors red, green, and blue are not properly superposed when a picture of a moving object is displayed, and a red or green tinge is therefore seen to trail after the moving object.
Typically, by increasing the switching speed of the light source color, i.e., raising the subfield frequency of the RGB field, color breaking can be reduced. For example, increasing the subfield by a factor of ten reduces the amount of color breaking (color breakup amount) to one tenth.
In Patent Document 2, a single-panel DLP (Digital Light Processing) projector is disclosed in which the subfield frequency is raised to reduce color breaking. “DLP” is a registered trademark.
A DLP projector has: a semiconductor laser, a phosphor wheel that is provided with a phosphor region, a scanning body that scans the phosphor region with a laser light from the semiconductor laser, a micromirror element such as a DMD that modulates the fluorescent light supplied from the phosphor region to form an image, and a projection lens that projects this image.
The micromirror element is driven by a pulse-width modulation (PWM) method and is capable of 256-(8-bit) gradation display. According to PWM 8-bit gradation display, one image (one field) is made up of eight binary images (subfields). In each subfield, weighting of each subfield can be implemented (i.e., luminance is varied) by the temporal length of the interval that a mirror is ON (lighted up), or by the number of pulses of lighting in this interval. Each subfield has a weighting (luminance) of “1,” “2,” “3,” “4,” “8,” “16,” “32,” “64,” and “128” according to the binary system. The micromirror element displays half-tones by means of the combinations of subfields that are lighted.
The phosphor region is divided into 72 parts in the circumferential direction, red phosphor regions, green phosphor regions, and blue phosphor regions being sequentially arranged in the divided regions. The red phosphor regions contain a phosphor that emits red fluorescent light upon excitation by laser light. The green phosphor regions contain a phosphor that emits green fluorescent light upon excitation by laser light. The blue phosphor regions contain a phosphor that emits blue fluorescent light upon excitation by laser light.
When the phosphor wheel is caused to rotate at 7200 revolutions/minute and the phosphor regions are scanned by laser light, red fluorescent light, green fluorescent light, and blue fluorescent light are sequentially emitted from the phosphor wheel. In this case, the frequency of repetition of the red, green, and blue fluorescent light (subfield frequency) is 2880 Hz and is equivalent to forty-eight times the speed of a case in which the frequency of repetition of color at double speed is set to 60 Hz. At this multiple of speed, color breaking can be reduced.